In-situ visualization of exhaust soot particle deposition and removal in channel flows

Exhaust gas recirculation (EGR) coolers are used in diesel engines to reduce emissions of nitrogen oxides. Thermophoretic particle deposition occurring in EGR coolers causes a significant degradation in the cooler effectiveness generally followed by the stabilization of cooler effectiveness after long exposure times. Mechanisms responsible for this stabilization are not clearly understood. To investigate the stabilization trend, a visualization test rig was developed to track the dynamics of diesel exhaust soot particulate deposition and removal in-situ. A digital microscope records surface characteristics. A medium duty engine is used to generate the exhaust stream. A steady state condition was selected to run the engine for the deposition tests. In contrast to conventional understanding, large particles (tens of microns) were observed in diesel exhaust. Interesting results are observed for flaking/removal of the deposit layer during designed removal experiments. Water condensation at a low coolant temperature and bombardment of large particles resulted in a significant removal of deposit in the form of flakes while thermal expansion or shear force (low velocities) alone did not remove the deposit layer. ► A unique apparatus for in-situ observation of thermophoretic particle deposition. ► In-situ measurement of the deposit layer (formed by nano-particles) thickness. ► Practical methods for removal of the formed layer in laminar channel flows. ► Observing micron size particle in diesel exhaust in contrast to conventional wisdom.